This invention relates to novel tetraacid ester compounds derived from halo-oxy- or dioxyphthalic anhydrides. The products are useful chemical intermediates for the further preparation of various compounds such as the corresponding tetracarboxylic acids and the various derivatives thereof. The esters of this invention are particularly useful as industrial plasticizers for polyvinyl chloride and polystyrene resins. Especially useful for this purpose are the alkyl esters, wherein the alkyl chain is 7-9 carbon atoms. Dioxydiphthalic diesters, wherein ester groups are on opposite phthalic acid groups are useful in the preparation of polyimides.
U.S. Pat. No. 4,697,023 discloses the preparation of oxydiphthalic anhydrides and suggests their use in the preparation of polyimides. The oxydiphthalic anhydrides are prepared by the reaction of a halophthalic anhydride with water and an alkali metal compound such as KF, CsF, or K.sub.2 CO.sub.3 in the presence of a polar aprotic solvent.
Kolesnikov, G. S. et al, Vysokomol. Soyed, A9, 612-18 (1967); Marvel, C. S. et al, J. Am. Chem. Soc., 80, 1197, (1958); and Latrova, Z. N. et al, Volokna Sin. Polim., 15-24 (1970), disclose the preparation of oxydiphthalic acids and anhydrides by the oxidation of tetramethyldiphenyl ethers.
German patent No. 2,416,594 (1975) discloses the preparation of 3,3'-oxydiphthalic anhydride by coupling of 3-nitrophthalic anhydride in the presence of metal nitrites such as sodium nitride.
U.S. Pat. No. 3,879,428 to Heath et al discloses the preparation of various aromatic bis(ether anhydrides) by reaction of nitrophthalimide with an alkali diphenoxide followed by hydrolysis and dehydration to yield the diether anhydride.
Tilika et al, Synthesis of Carboxylic Acids of Aromatic Sulfides, Latv. PSR Zinat. Akad. Vestis, Kim. Ser. (2), 201-4, 1982; CA 97(7):55412U, disclose the reaction of 5-bromo-4-mercaptophthalic acid with Cu.sub.2 O to give 80 percent thianthrene-2,3,7,8-tetracarboxylic acid, that is, ##STR2##
Pebalk et al, Spin Density Distribution In Anion Radicals of Aromatic Tetracarboxylic Acid Dianhydrides, Dokl. Akad Nauk, SSR, 244(5), 1169-73, [Phys. Chem.] 1979; CA 90(23):186029c, disclose the EPR spectra of various compounds including a compound of the structure ##STR3##
Pebalk et al, Electron-acceptor Properties of Aromatic Dianhydrides, Dokl. Akad. Nauk, SSR, 236(6), 1379-82, [Chem.] 1977; CA 88(19):135960a, disclose the electron-acceptor properties of 15 phthalic anhydrides and condensed phthalic anhydrides including dithio-diphthalic anhydrides.
2,3,7,8-Tetracarboxyphenoxathin dianhydride of the formula ##STR4## is disclosed by Erglis et al., (USSR Patent No. 395,358; CA 80(9):48007m). The compound was prepared by the reaction of (3,4-Me.sub.2 C.sub.6 H.sub.3).sub.2 O with sulfur in the presence of aluminum chloride followed by oxidation with KMnO.sub.4 in aqueous piperidine to form the tetracarboxylic acid, which was cyclized.